The very large majority of current navigation terminals use a satellite positioning system (SPS) such as GPS (Global Positioning System). Hereafter we will use the term “positioning” when a terminal determines its geographical position owing to signals it receives and, conversely, the term “localization” when the coordinates of a terminal are determined by the signals it emits.
In urban environment, the presence of buildings disturbs the propagation of satellite signals through occultation, reflection, attenuation and diffraction effects. Thus, the positioning performance of the SPS is damaged both in terms of availability and precision.
In order to resolve these drawbacks, it has been proposed to use the radiofrequency signals emitted by wireless telecommunications systems, widely used in urban areas, to determine the position of a mobile terminal. For example, the article by G. Boriello et al. entitled “Delivering real-world ubiquitous location systems,” available at www.placelab.org/publications/, describes a positioning system (Place Lab project) using the signals emitted by the access points of a Wi-Fi network (IEEE 802.11). In that system, the terminal first scans the Wi-Fi access points within range and thereby obtains their MAC addresses as well as the respective powers or RSS (Received Signal Strength) of the received signals. The terminal then searches from those MAC addresses for the geographic positions of the access points and performs a barycentric weighting thereof with the powers in question to estimate its own position.
This positioning system is not, however, fully satisfactory inasmuch as the precision of the positioning is still insufficient. Furthermore, the calculated positions are sometimes absurd in that they can correspond to inaccessible zones, which damages the reliability of the system. Lastly, it requires viewing a database containing the list of access points and their respective geographic positions. The data can be collected collaboratively or in a centralized manner. In collaborative collection, individuals having portable Wi-Fi/GPS terminals provide, during their movement, their positions and their Wi-Fi scan results at those locations (MAC addresses and RSS levels). In a centralized collection, vehicles equipped with GPS receivers and Wi-Fi terminals criss-cross the zone to be mapped following a predetermined diagram to collect the MAC addresses and RSS levels. This collection strategy makes it possible to have complete coverage of the zone and to eliminate certain positioning artifacts created by a non-homogenous distribution of the access points inventoried in the database. The data collection, whether collaborative or centralized, is, however, a slow and expensive process. Furthermore, it must be done continuously or at regular intervals so as to update the access points.
The aim of the present invention is to propose a positioning system using the access points of a wireless telecommunications system that does not have the aforementioned drawbacks, in particular that improves the precision and reliability of the positioning. One subsidiary aim of the present invention is to propose a method for forming the database that is fast, effective and inexpensive.